Hydrostatic transmission control

ABSTRACT

An improved apparatus for controlling the operation of a plurality of hydrostatic transmissions includes a single-control member. The control member is connected with the hydrostatic transmissions by a mechanical linkage which enables the control member to be moved in a natural manner to control both forward and reverse movement of a vehicle driven by the hydrostatic transmissions. The mechanical linkage can be used with different types of control members, such as a joystick or a T-handle.

United States atet Inventor Robert B. Lauck Southfield, Mich.

App]. No. 823,787

Filed May 12, 1969 Patented Dec. 7, 1971 Assignee Eaton Yale & TowneInc.

Cleveland, Ohio HYDROSTATIC TRANSMISSION CONTROL 31 Claims, 11 DrawingFigs.

US. Cl ISO/6.48, 74/471 XY, 180/77 H Int. Cl B62d 11/04 Field of Search180/648, 6.5; 74/471 R. 471 XY, 77 H References Cited UNITED STATESPATENTS 6/1960 Bowers et al.

3,323,607 6/1967 Futamata 74/471 XY 3,431,993 3/1969 Case 180/6483,181,389 5/1965 Richard 74/480 Primary Examiner-Benjamin HershAssistant Examiner-John A. Pekar Allorney- Yount & Tarolli ABSTRACT: Animproved apparatus for controlling the operation ofa plurality ofhydrostatic transmissions includes a single-control member. The controlmember is connected with the hydrostatic transmissions by a mechanicallinkage which enables the control member to be moved in a natural mannerto control both forward and reverse movement of a vehicle driven by thehydrostatic transmissions. The mechanical linkage can be used withdifferent types of control members, such as ajoystick or a T-handle.

PATENTED DEC 7 I97! SHEET 1 [1F 3 FIGS FIG 5 x mwwm 4/. N i m M. r 0v 7L m IIYDROSTATIC TRANSMISSION CONTROL This invention relates generallyto a control system and more particularly to a control system for aplurality of hydrostatic transmissions.

A known vehicle-steering and speed control system includes a singlemember which is manually actuated to control the speed and direction ofoperation of a plurality of hydrostatic transmissions. This controlmember is connected with the hydrostatic transmissions my means of amechanical linkage. To effect a turning of the vehicle toward the leftwhile it is going forward, the control member is moved toward theoperators left However to effect a turning of the vehicle toward theleft while it is going backward, the control member must be moved towardthe operators right. The necessity of moving the control member towardthe right to effect a left turn while the vehicle is going backwardrequires the operator to move the control member in a manner which iscontrary to his natural instincts. This unnatural movement of thecontrol member is necessitated by the inherent operation of knownmechanical linkage arrangements for interconnecting the single controlmember and the hydrostatic transmissions.

Accordingly, it is an object of this invention to provide a new andimproved mechanical linkage for operatively connecting a plurality ofhydrostatic transmissions with a singlecontrol member which is moved ina natural manner to control the direction and speed of forward andreverse movement of a vehicle.

Another object of this invention is to provide a new and improvedmechanical linkage which is suitable for use with different types ofcontrol members, such as a joystick or a T-handle, to control operationof a plurality of hydrostatic transmissions and thereby vary the speedand direction of forward and reverse movement of a vehicle in a mannerwhich corresponds directly to the direction of operation of the controlmember.

Another object of this invention is to provide a new and improvedapparatus for controlling the operation of a plurality of hydrostatictransmissions including a single-control member which is operableforwardly or rearwardly from an initial position to actuate a mechanicallinkage and thereby effect operation of the hydrostatic transmissions ineither the forward or the reverse direction at a speed which is variedby varying the extent of operation of the control member, the controlmember being operable in a third direction after operation in either theforward or reverse direction to decrease the speed of operation of onehydrostatic transmission relative to another hydrostatic transmission.

Another object of this invention is to provide a new and improvedapparatus as set forth in the next preceding object and wherein thecontrol member is operable in a fourth direction after operation ineither the forward or reverse direction to decrease the speed of theother hydrostatic transmission.

These and other objects and features of the invention will become moreapparent upon a consideration of the following description taken inconnection with the accompanying drawings wherein:

FIG. 1 is a schematic illustration of an assembly for controlling theoperation of a plurality of hydrostatic transmissions for driving avehicle;

FIG. 2 is a sectional view of the control assembly of FIG. 1illustrating the relationship between a manually actuatable controlmember and a mechanical linkage assembly;

FIG. 3 is a fragmentary plan view further illustrating the structure ofthe mechanical linkage assembly of FIG. 2;

FIG. 4 is a plan view of a main actuator link or lever of the mechanicallinkage assembly of FIGS. 2 and 3;

FIG. 5 is a plan view of a right actuator link or lever of themechanical linkage assembly of FIGS. 2 and 3;

FIG. 6 is a sectional view of a slip-type coupling or link of themechanical linkage assembly;

FIG. 7 is an elevational sectional view, taken generally along the line7-7 of FIG. 2, illustrating the relationship the control member to aconnector or drive assembly for operatively connecting the controlmember with the mechanical linkage assembly;

FIG. 8 is a schematic illustration of the mechanical linkage assembly inan actuated condition for effecting forward movement of the vehicle;

FIG. 9 is a schematic illustration, similar to FIG. 8, of the mechanicallinkage assembly in an actuated condition for effecting reverse movementof the vehicle;

FIG. 10 is a schematic illustration, similar to FIG. 9, illustrating themechanical linkage assembly in an actuated condition for effecting areverse left turning of the vehicle; and

FIG. 11 is an illustration of a second embodiment of the inventionwherein the control member is a T-handle.

The present invention provides an apparatus for controlling theoperation of a plurality of hydrostatic transmission for driving avehicle. The apparatus includes a single control member, such as ajoystick or T-handle, which is connected with the hydrostatictransmissions by a mechanical linkage assembly. This mechanical linkageassembly effects operation of the hydrostatic transmissions to provide anatural relationship between operation of the control member andmovement of a vehicle. Thus, when the control member is operated to theleft the vehicle is turned to the left whether it is going forward orbackward. Similarly, if a control member is operated toward the right,the vehicle is turned to the right whether it is going forward orbackward.

A control assembly 20 (FIG. 1) is operable to control the operation of apair of hydrostatic transmissions for driving a vehicle, such as acrawler or tractor. Each of the hydrostatic transmissions is associatedwith one of the tracks of the crawler in a known manner and is driven bya suitable source of power to efiect movement of the vehicle in responseto actuation of a single-control member 22. The control member orjoystick is connected with the hydrostatic transmissions by a mechanicallinkage assembly 24.

The mechanical linkage assembly 24 enables the control member 22 to bemoved in a natural manner to control forward and reverse movement of thevehicle. Thus, to effect a forward and left-tuming movement of thevehicle, the control member 22 is moved forwardly and to the operator'sleft. To effect rearward and left turning movement of the vehicle thecontrol member 22 is moved rearwardly and to the operators left. A rightturn is effected in either the forward or reverse directions by movingthe control member forwardly or rearwardly and to the right. The speedof movement of the vehicle in any given direction is controlled byvarying the extent to which the control member 22 is operated in thegiven direction.

This direct correspondence between the direction of movement of thecontrol member 22 and the direction of movement of the vehicle isprovided for by the mechanical linkage assembly 24. The linkage assembly24 is mechanical, that is it is formed by a plurality of mechanicallyinterconnected links and is devoid of hydraulic and electricalcomponents. These mechanically interconnected links include right andleft connector rods or links 28 and 30. The right connector rod 28 ismovable to control the direction and speed of operation of a righthydrostatic transmission, that is the hydrostatic transmissionassociated with the right track of the vehicle. Similarly, the leftconnector rod or link 30 is movable to control the speed and directionof operation of a left hydrostatic transmission, that is the hydrostatictransmission associated with the left track of the vehicle. Although thelinkage assembly 24 is mechanical so that it has no hydrauliccomponents, the connector rods 28 and 30 can effect operation of thehydrostatic transmissions through suitable control valves or servomotorsin a manner illustrated in my copending application Ser. No. 7 l6,204,filed on Mar. 26, 1968 and entitled Hydrostatic Transmission ControlSystem.

Upon straight forward movement of the control member 22, the mechanicallinkage assembly 24 moves the connector rods 28 and 30 rearwardly forthe same distance to effect operation of the hydrostatic transmissionsat the same speed in the forward direction. Movement of the controlmember or joystick 22 backwardly or in a reverse direction moves theconnector rods 28 and 30 forwardly for substantially the same distanceto effect operation of the hydrostatic transmissions at the same speedin the reverse direction. The extent to which the connector rods 28 and30 are moved and the speed of operation of a hydrostatic transmissions,is a direct function of the extent of movement with the control member22 in either the forward or reverse direction.

The mechanical linkage assembly 24 includes a main actuator lever orlink 34 (see FIG. 1-4) which is pivoted about a mounting 36 to effectequal movement of right and left actuator links or levers 40 and 42about the pivot mounting 36. This movement of the actuator links 40 and42 is transmitted to the connector rods 28 and 30 to move them throughthe same distance and effect operation of the hydrostatic transmissionat the same speed and in the same direction. The right actuator link 40(FIG. is pivotal relative to the main actuator lever 34 to decrease thespeed of operation of the right hydrostatic transmission relative to theleft hydrostatic transmission and thereby effect a rightward turningmovement of the vehicle. Similarly, the left actuator link 42 (FIG. 1)is pivotal relative to the main actuator link 34 to decrease the speedof operation of the left hydrostatic transmission relative to the righthydrostatic transmission to thereby effect a leftward turning movementof the vehicle. This pivoting movement of the right and left actuatorlinks 40 and 42 relative to the main actuator link 34 is effected bypivoting right and left-turn links 46 and 48 that are fixedlyinterconnected on the common mounting 36. The turn links 46 and 48 arepivoted together relative to the main actuator link 34 by means of anoperator rod 52 which is pivotally connected to the left-turn link 48.

When the control member 22 is operated toward the right, the rightactuator link 40 is actuated through a right slip link or coupling 56(FIG. 6) which is pivotally connected between the right-tum link 46 andright actuator link. Similarly, the left-turn link 48 is connected withthe left actuator link 42 by a left slip link or coupling 58 (FIG. 1)which is pivotally connected to the left-turn link and left actuatorlink. Movement of the actuator links 40 and 42 under the influence ofthe associated slip links 56 and 58 is translated to the connector rods28 and 30 by connector links 62 and 64.

Upon movement of the control member 22 toward the left, the operator rod52 pivots the interconnected turn links 46 and 48 in a clockwisedirection as viewed in FIGS. 1 and 2. This pivotal movement of the leftturn link 48 causes the left slip link or coupling 58 to pivot the leftactuator link 42 in a generally clockwise direction relative to the mainactuator link 34. When the control member 22 is moved to the left fromthe neutral or initial position illustrated in FIGS. 1 and 2, a pivotconnection 68 between the connector rod 30 and the connector link 64 iscoaxial with the pivot mounting 72 of the left actuator link 42 on themain actuator link 34. This results in the left actuator link 42 andconnector link 64 merely spinning about their common axis withoutefiecting movement of the connector rod 30 upon leftward movement of thecontrol member from its initial position. Therefore, the lefthydrostatic transmission remains in its neutral condition. Similarly,when the control member 22 is moved to the right from the neutral orinitial position, a pivot connection between the connector rod 28 andthe connector link 62 is coaxial with the pivot mounting for the rightactuator link 40. Therefore, the connector link 28 is not moved inresponse to this movement of the actuator link 40 and the righthydrostatic transmission remains in its neutral condition.

Movement of the control member 22 to the right or the left is effectiveto turn the vehicle when the control member has previously been movedeither forwardly or rearwardly from its initial position. When thecontrol member 22 is moved forwardly from the initial position, anoperator rod 76 pivots the main actuator link 34 in a counterclockwisedirection from the initial position of FIG. I so that the main actuatorlink assumes an orientation similar to that shown in FIG. 8 This pivotalmovement of the main actuator link 34 pivots the left actuator link 42in a counterclockwise direction about the pivot mounting 72 and thepivot connection 74 moves rearwardly of the initial position shown inFIG. I. This causes the pivot connection 68 between the connector rod 30and connector link 64 to move rearwardly, through the distance indicatedby the arrow in FIG. 8, to thereby operate a suitable servomechanism toeffect forward operation of the left hydrostatic transmission. Ofcourse, the speed at which the left hydrostatic transmission operates inthe forward direction varies as a function of the extent of movement ofthe control member 22 in the forward direction from the initial positionof FIG. 1. Since it has been assumed that the control member 22 wasmoved straight forwardly, the right connector rod 28 is moved rearwardlyby operation of the right actuator link 40 and connector link 62 tothereby effect operation of the right hydrostatic transmission in theforward direction.

Movement of the control member 22 toward the left, after it has beenmoved forwardly from the initial position of FIG. I, actuates themechanical linkage 24 to decrease the speed of operation of the lefthydrostatic transmission. If the control member is moved as far aspossible toward the left, the mechanical linkage 24 effects operation ofthe left hydrostatic transmission in the reverse direction at a speedwhich is equal to the speed at which the right hydrostatic transmissionis operated in the forward direction. This results in a sharp turning orspinning of the vehicle toward the left.

When the control member 22 is moved toward the left from the forwardoperated position of FIG. 8, the operator rod 52 pivots the turn link 48in a clockwise direction as viewed in FIG. 1. This movement of the turnlink 48 is transmitted to the left actuator link 42 by the slip link orcoupling 58 which effects pivotal rotation of the left actuator link 42in a clockwise direction as viewed in FIG. 8 about the pivot connection72. This pivoting of the left actuator link 42 moves the pivotconnection 74 upwardly and forwardly from the forward operated positionof FIG. 8 to thereby move the pivot connection 68 forwardly toward theneutral or initial condition of FIG. 1. Of course, this results in thespeed of the left hydrostatic transmission being decreased to cause aleftward turning of the vehicle.

If the control member 22 is moved or operated toward the left for halfof its maximum leftward stroke, the pivot connection 68 is moved to theinitial position illustrated in FIG. 2. The left hydrostatictransmission is then deswashed to its neutral condition so that it isineffective to transmit power to the left track of the vehicle. Theright track then causes the vehicle to turn in a hard left turn.Continued movement of the control member 22 toward the left moves thepivot connection 68 forwardly of the initial position of FIGS. I and 2to thereby effect operation of the left hydrostatic transmission in thereverse direction and a spinning of the vehicle toward the left. Whenthe control member 22 has been operated through its maximum leftwardstroke, the left hydrostatic transmission operates in the reversedirection at the same speed at which the right hydrostatic transmissionoperates in the forward direction.

Although the left actuator link 42 was pivoted relative to the mainactuator link 34 in response to the leftward movement of the controlmember 22, the right actuator link 40 remained stationary relative tothe main actuator link 34. This is because the turn link 46 is connectedwith the right actuator link 40 by the slip link or coupling 56. Theslip link 56 (FIG. 6) and includes a body or block end which ispivotally connected by a pin 82 to the right actuator link 40. A rod end86 of the slip link 56 is pivotally connected by a pin 88 to the turnlink 46. A stop ring 90 is mounted on the rod 86 to enable the slip link56 to push or pivot the right actuator link in a clockwise direction asviewed in FIG. I when the slip link 56 is moved away from the pivotconnection between therslip link and the right actuator link 40. Howeverwhen the pivot connection between the slip link 56 and the turn link 46is moved away from the pivot connection between the slip link and theright actuator link 40, the rod 86 merely slides outwardly relative tothe block 80 and the slip link 56 is expanded without effecting movementof the right actuator link 40.

When the control member 22 is moved toward the left, the interconnectedturn links 46 and 40 are both pivoted in a clockwise direction. However,the clockwise pivoting movement of the turn link 46 effects an expandingof the slip link 56 without pivoting the right actuator link. Therefore,when the control member 22 is moved toward the left, the slip link 56effectively absorbs the movement of the turn link 46 so that the rightconnector rod 28 remains stationary and right hydrostatic transmissioncontinues to operate at its previous speed. The left slip link 53 hasthe same construction as the right slip link 56. The slip link 50 iseffective to transmit motion from the turn link 40 to the left actuatorlink 42 upon leftward actuation of the control member 22. However, theslip link 58 expands upon rightward movement of the control member 22 sothat the left hydrostatic transmission is uneffected by this movement.

Operation of a control member 22 in the reverse direction actuates themechanical linkage 24 in a generally similar but opposite manner-to thatin which it is actuated by forward movement of the control member 22.Thus, upon reverse movement of the control member 22 the mechanicallinkage 24 is actuated to move the right and left connector rods 28 and30 equal distances in the forward direction to effect operation of thehydrostatic transmissions in the reverse direction at the same speed.Movement of the control member 22 is the reverse direction pivots themain actuator link 34 in a clockwise direction about the pivotconnection 36 from the initial position shown in FIG. 2 to the reverseactuated position shown in FIG. 9. The reverse or rearward movement ofthe control member 22 also pivots the turn links 46 and 48 in aclockwise direction from their initial positions. The pivotal movementof the left-turn link is transmitted to the left actuator link 42 by theleft slip link 50. This pivots the left actuator link 42 about the pivotconnection '72 in a generally clockwise direction from the initialposition of FIG. ll.

The combined effect of the pivotal movement of the main actuator link 34and the left actuator link 42 moves the pivotal connection 74 on theconnector link 64 forwardly. Therefore, the pivot connection 68 betweenthe connector rod 30 and the connector link 64 is moved forwardly,through the distance indicated by the arrow in FIG. 9, to effectactuation of the left hydrostatic transmission in the reverse direction.Similarly, the right actuator link 40 is pivoted downwardly and in agenerally clockwise direction by the combined effect of the pivotingmovement of the main actuator link 34 and the turn link 46. Therefore,the pivot connection between right connector link 62 and the rightconnector rod 28 moves forwardly. Both of the connector rods 28 and 30are moved through the same distance so that the left and righthydrostatic transmissions are operated in the reverse direction at thesame speed to move the vehicle straight rearwardly.

Actuation of the control member 22 to effect a left turn while thevehicle is moving rearwardly operates the mechanical linkage 24 to movethe pivot connection 68 from the reverse actuated condition of FIG. 9toward the neutral position of FIG. 2 to thereby effect a decrease inthe speed of the left hydrostatic transmission. If the control member ismoved as far to the left as possible, the pivot connection 68 movesthrough the initial or neutral position (shown in FIG. toward theforward actuated position of FIG. 8. This effects operation of the lefthydrostatic transmission in the forward direction at a speed which isequal to the speed at which the right hydrostatic transmission isoperated in a reverse direction to thereby spin the vehicle upon itscentral axis.

Upon operation of the control member 22 toward the left, the turn link40 is pivoted in a clockwise direction by the operator rod 52. The sliplink 58 then pivots the left actuator link 42 clockwise direction fromthe position shown in FIG. 9 to the position shown in FIG. it). As theactuator link 42 pivots in a clockwise direction, the pivot connection60 is moved rearwardly from the position in FIG. 9 toward the positionshown in FIG. 10. When the pivot connection reaches the position shownin FIG. I0 it is in the neutral or initial position of FIG. 2.Therefore, the left hydrostatic transmission is actuated to a neutralcondition by the connector rod 30. Continued leftward movement of thecontrol member 22 causes the connector rod 30 to actuate the lefthydrostatic transmission to a forward operating condition.

The right turn link 46 is also pivoted in a clockwise direction inresponse to the leftward movement of the control member 22. However, theslip link 56 is expanded in the manner previously explained and theright actuator lever 40 remains stationary relative to the main actuatorlink 34. Therefore, the right connector rod 28 is not moved in responseto the leftward movement of the control member 22 and the righthydrostatic transmission continues to operate at a constant speed in thereverse direction.

If the control member 22 is moved toward the right while the vehicle ismoving in a reverse direction, the mechanical linkage 24 operates theright connector rod 28 to decrease the speed of a right hydrostatictransmission while the left hydrostatic transmission continues tooperate at a constant speed in the reverse direction. When the controlmember 22 is moved toward the right, the turn links 46 and 48 arepivoted in a counterclockwise direction. The counterclockwise pivotingmovement of the right turn link 46 is transmitted by the right slip link56 to the right actuator lever 40 which is pivoted in a clockwisedirection from the position shown in FIG. 9. This moves the pivotconnection between the connector link 62 and right connector rod 28rearwardly to thereby effect a decrease in the speed of the righthydrostatic transmission. When the control member is moved to the rightas far as possible, the connector rod 28 is moved through its initialposition to effect operation of the right hydrostatic transmission in aforward direction at a speed which is equal to the speed at which theleft hydrostatic transmission is operating in the reverse direction. Ofcourse, the counterclockwise pivoting movement of the turn link 48causes an expansion of the left slip link 58 so that the left actuatorlink is not pivoted relative to the main actuator link 34 and the speedof the left hydrostatic transmission remains substantially constant.

The control member or joystick 22 actuates the mechanical linkage 24through a connector or drive assembly T00 (FIG. 1 The connector or driveassembly includes an outer actuator shaft 102 having a cage or carrier104 on which the control member 22 is pivotally mounted by means of asupport rod or shaft 106. A gear assembly 108 connects the controlmember 22 with an inner actuator shaft 112. Upon movement of the controlmember 22 toward the right or the left, the inner actuator shaft 112 isrotated by the gear assembly 1108. The gear assembly 108 includes a gear116 which is fixedly connected to the support shaft 106 and a gear 1 18which is fixedly connected to the inner actuator shaft 112. Uponmovement of the control member 22 toward the left from the initialposition shown in FIG. 1, the gear 116 is rotated toward the left toeffect generally clockwise rotation of the gear 110 and actuator shaft112. Similarly, when the control member is moved toward the right thegear 116 is rotated toward the right and efiects counterclockwiserotation of the actuator shaft 112.

The actuator shafts I02 and 112 are both rotated by movement of thecontrol member 22 in either the forward or reverse direction. Thus, ifthe control member 22 is moved forwardly the cage 104 is rotated in agenerally counterclockwise direction as viewed in FIG. 1. The gears 116and 118 do not rotate relative to each other so that the shaft 112 isalso rotated in a counterclockwise direction. Similarly, when thecontrol member 22 is moved in the reverse direction, the actuator shaftsI02 and i112 are rotated in a clockwise direction. Movement of theactuator member 22 from the ini tial position is limited by a bracket122 which is engaged by a stop pin 126 connected to the control member22. The rotational movement of the actuator shafts I02 and H2 istransmitted by the operator rods 52 and 76 to the mechanical linkage 24.Thus, the outer actuator shaft 102 has a downwardly projecting actuatorlever 130 which is pivotally connected with the operator rod 76.Similarly, a downwardly projecting actuator lever 132 is fixedly securedto the inner actuator shaft 112 and is pivotally connected with theoperator rod 52.

From the foregoing description, it is apparent that when the controlmember 22 is moved forwardly the actuator levers 130 and 132 are pivotedin a generally clockwise direction as viewed in FIG. 1. This moves theoperator rods 76 and 52 rearwardly and effects a pivoting movement ofthe main actuator link 34 and turn links 46 and 48 in a counterclockwisedirection to the forward actuated position of FIG. 8. 1f the controlmember 22 is then moved toward the left, the gear 116 drives the gear118 in a generally clockwise direction as viewed in FIG. 1 to pivot theturn links 46 and 48. Since the control member 22 is being pivoted aboutthe longitudinal axis of the support shaft 106 as it is moved toward theleft, the carrier or cage 104 is not pivoted about the longitudinal axisof the actuator shaft 102. Therefore, the actuator lever 130 remainsstationary and the main actuator link 34 stays in the forward operatedposition to which it had been previously actuated by forward movement ofthe control member 22. Of course, rightward movement of the controlmember 22 results in the gear 118 being driven in a counterclockwisedirection by the gear 116 to pivot the actuator lever 132 in acounterclockwise direction. This moves the turn links 46 and 48 in acounterclockwise direction and efiects a right-tuming of the vehicle inthe manner previously explained.

The outer actuator shaft 102 is biased toward an initial or neutralposition by a double-acting spring box 140 is pivotally connected at oneend to an actuator lever 142 which extends downwardly from the outershaft 102 and is connected to a fixed member at its opposite end.Therefore when the control member 22 is moved in either the forward orreverse directions and released, the spring box 140 returns the controlmember to the initial or neutral position. A pair of biasing springs 146and 148 (FIGS. 1 and 3) are connected at their inner ends to the mainactuator link 34 and at their outer ends to the right and left actuatorlinks 40 and 42 to bias the actuator links to their initial positions.Therefore, if the control member 22 is moved either the right or theleft and released, the actuator springs 146 and 148 operate through themechanical linkage 24 to return the control member 22 to the initialposition.

A retaining assembly 152 is selectively operable to maintain the controlmember 22 in a position corresponding to a desired speed in the forwardor reverse directions. The retainer assembly 152 includes a pressurehead 154 having the friction member 156 for engaging a sector 158 whichis fixedly mounted on the outer actuator shaft 102 (See FIG. 1). Theopposite end of the pressure head 154 is mounted in threaded engagementwith a body 160. The body 160 is fixedly connected to an actuator knob162 so that rotation of the knob 162 moves the pressure head 1S4 axiallyrelative to the sector 158.

When the control member 22 has been operated to a position correspondingto a desired speed in either the forward or reverse directions, the knob162 is rotated to press the friction member 156 against the sector 158.This presses the sector 158 against a friction pad 163 to hold the outeractuator shaft 102 and the control member 22 against pivotal movementback to the initial condition under the influence of the spring box 140.When it is desired to move the control member 22 to vary the speed ofthe vehicle, the knob 162 is rotated to move the pressure head 154axially away from the sector 158 so that the friction member 156 nolonger presses the sector against the friction pad 163.

in the specific preferred embodiment of the invention illustrated inFIGS. 1 through 7 the control member 22 is a joystick which is rotatedabout one axis, i.e. the longitudinal axis of the actuator shafts 102and 112, to vary the speed of operation of the hydrostatic transmissionsin the forward and reverse directions. The joystick 22 is rotated abouta second axis, i.e. the longitudinal axis of the support shaft 206, todecrease the speed of one of the hydrostatic transmissions relative tothe other and effect a turning of the vehicle. The

mechanical linkage 24 effects the operation of the hydrostatictransmission so as to enable the control member 22 to be moved in anatural manner to control both the speed and direction of movement ofthe vehicle.

In the embodiment of the invention illustrated in FIG. 11, the controlmember takes the form of a T-handle which is rotatably mounted on acarrier or cage 182. The cage 182 is connected to an outer actuatorshaft 184 in much the same manner as in which the carrier or cage 104 isconnected with the outer actuator shaft 102. Upon forward or reversemovement of the T-handle, that is in the direction indicated in thearrows in FIG. 11, the outer actuator shaft 184 is rotated to effectoperation of a mechanical linkage to vary the speed of operation of apair of hydrostatic transmissions in the same way as previouslyexplained in connection with the mechanical linkage 24.

The T-handle 180 is rotated to either the right or to the left to effecta turning of the vehicle by decreasing the speed of one of thehydrostatic transmissions relative to the other. Thus if the T-handle180 is rotated to the right about the longitudinal axis of the stem orbody portion 188 of the T-handle, the associated mechanical controllinkage is operated to decrease the speed of the right hydrostatictransmission and effect a right turning of the vehicle in either aforward or a reverse direction. Similarly if the T-handle 180 is rotatedtoward the left about its longitudinal axis the speed of operation ofthe left hydrostatic transmission is decreased to turn the vehicletoward the left. When the T-handle 180 is in the initial or neutralcondition and is operated to either the right or left, the T-handle isineffective to vary the speed of either of the hydrostatictransmissions. This is because the associated mechanical linkageoperates in the same manner as the mechanical linkage 24 and isineffective to actuate the hydrostatic transmissions.

The T-handle 180, like the joystick 22, is moved in a natural manner tocontrol both the speed and direction of movement of a vehicle. TheT-handle 180 is mounted on a support shaft 192 which extends through aninner actuator shaft 194. A gear sector or segment 196 is connected tothe outer end of the inner actuator shaft 194 and is rotated about thelongitudinal axis of the inner actuator shaft by a pinion gear 198 whichis fixedly connected with the stern 188 of the T-handle 180. Uponrotation of the T-handle 180 to either the right or the left, the gear198 drives the gear segment 196 to rotate the inner actuator shaft aboutits longitudinal axis in much the same manner as in which the inneractuator shaft 112 is rotated about its longitudinal axis by the gearassembly 108. A retainer assembly 200 of the same construction as theretainer assembly 152, is operable to engage a sector 202 to retain theT-handle 180 against movement from a selected forward or reverseoperated condition in the manner previously explained.

In view of the foregoing description, it can be seen that the presentinvention provides a mechanical linkage 24 which can be actuated by asingle control member, i.e. either the joystick 22 or T-handle 180, tocontrol the direction and speed of forward and reverse operation of aplurality of hydrostatic transmission in a natural manner. To providefor this operation of the hydrostatic transmissions, the control linkageincludes a main actuator link 34 which is operated from an initialposition to effect either forward or reverse operation of thehydrostatic transmissions at a speed which is a function of the extentof movement of the main actuator link from the initial position. Rightand left actuator links 40 and 42 are mounted on the main actuator link34 and are operable in response to right or left operation of thecontrol member to decrease the speed of the hydrostatic transmissionassociated with the direction in which the control member is operated.Thus, the control member is operated to the right and right actuatorlink 40 is operated to decrease the speed of the right hydrostatictransmission and effect a turning movement of the vehicle toward theright. Similarly, if the control member is operated to the left the leftactuator link 42 is operated to decrease the speed of the lefthydrostatic transmission and effect a turning movement of the vehicletoward the left. if the control member is operated to either the left orright while in its neutral or initial position, the mechanical linkage24 is ineffective to effect operation of hydrostatic transmissions fromthe neutral condition in which they are incapable of transmitting powerto the tracks of the vehicle.

The following is claimed:

1. Apparatus for controlling the operation of a plurality of hydrostatictransmissions, said apparatus comprising a singlecontrol member movablein a plurality of directions from an initial position for controllingthe speed and direction of operation of said hydrostatic transmissionsand for varying the speed of operation of said hydrostatic transmissionsrelative to each other, and linkage means for connecting said controlmember to said hydrostatic transmissions in such a manner that movementof said control member in either one of two lateral directions relativeto said initial position is ineffective to vary the operation of saidhydrostatic transmissions,

said linkage means comprising,

first and second actuator links mounted for pivotal movement about acommon axis,

first and second connector rods pivotally connected to said first andsecond actuator links respectively for actuation thereby upon movementthereof,

the pivotal connection between said first actuator link and said firstconnector rod and said second actuator link and said second connectorrod lying on said common axis when said control member is disposed ineither lateral direction from said initial position.

2. Apparatus as set forth in claim 1 wherein at least one of saidactuator links is movable about a first axis in response to movement ofsaid control member in any one of said plurality of directions tothereby effect a variation in the operation of one of said hydrostatictransmissions, said actuator link being movable about said common axisin response to movement of said control member in either one of said twolateral directions from said initial position without varying theoperation of said one hydrostatic transmission.

3. Apparatus as set forth in claim 2 wherein the other actuator link ismovable about a first axis in response to movement of said controlmember in any one of said plurality of directions to thereby effect avariation in the operation of another of said hydrostatic transmissions,said other actuator link being movable about said common axis inresponse to movement of said control member in either one of said twodirections from said initial position without varying the operation ofsaid other hydrostatic transmission.

4. Apparatus as set forth in claim 3 wherein said first axis about whichsaid actuator links rotate are coaxial.

5. Apparatus as set forth in claim 1 wherein movement of said controlmember in a first one of said plurality of directions effects operationof said hydrostatic transmissions at substantially the same speed in onedirection, said control member being movable in a second one of saidplurality of directions to effect operation of said hydrostatictransmissions at substantially the same speed in another directionopposite from said one direction, said control member being movable in athird one of said plurality of directions which is lateral to a path ofmovement of said control member in said first and second directions toeffect operation of one of said hydrostatic transmissions at a greaterspeed in said one direction than the speed at which another of saidhydrostatic transmissions is operated in said one direction, and saidcontrol member being movable in a fourth one of said plurality ofdirections which is lateral of said path of movement of said controlmember to effect operation of said one hydrostatic transmission at agreater speed in said other direction than the speed at which another ofsaid hydrostatic transmissions is operated in said one direction.

6. Apparatus as set forth in claim 1 further including drive means foractuating said linkage means in response to movement of said controlmember in any one of said plurality of directions and in either of saidtwo lateral directions.

Hill.

7. Apparatus as set forth in claim 1 further including gear meansoperatively interconnecting said control member and said linkage meansfor actuating said linkage means in response to movement of said controlmember in any one of said plurality of directions and in either of saidtwo lateral directions.

8. Apparatus set forth in claim 1 wherein said control member is movablein said plurality of directions from said initial position to aplurality of operating positions corresponding to various speeds anddirections of operation of said hydrostatic transmissions, said controlmember being movable in at least said two of said lateral directionsfrom any one of said operating positions to vary the speed of at leastone of said hydrostatic transmissions relative to another of saidhydrostatic transmissions.

9. Apparatus as set forth in claim 8 further including selectivelyactuatable retaining means for retaining said control member againstmovement in any one of a plurality of directions from a selected one ofsaid operating positions while allowing said control member to move inat least one of said two lateral directions from said selected one ofsaid operating positions.

I 10. Apparatus for controlling the operation of a plurality ofhydrostatic transmissions, said apparatus comprising a singlecontrolmember movable in a plurality of directions from an initial position forcontrolling the speed and direction of operation of said hydrostatictransmissions and for varying the speed of operation of said hydrostatictransmissions relative to each other, and linkage means for connectingsaid control member to said hydrostatic transmissions in such a mannerthat movement of said control member in either one of two directionsrelative to said initial position is ineffective to vary the operationof said'hydrostatic transmissions, said linkage means including firstactuator means for contemporaneously effecting substantially equalvariations in the operating speed of each of said hydrostatictransmissions in response to movement of said control member, secondactuator means for ef fecting variations in the operating speed of oneof said hydrostatic transmissions without effecting correspondingvariations in the speed of another of said plurality of hydrostatictransmissions, and third actuator means for effecting variations in theoperating speed of said other hydrostatic transmission without effectingcorresponding variations in the speed of said one hydrostatictransmission.

lll. Apparatus as set forth in claim 10 wherein said second actuatormeans is actuated in response to movement of said control member in oneof said two directions and said third actuator means is actuated inresponse to movement of said control member in the other of said twodirections.

12. Apparatus as set forth in claim 10 wherein said linkage meansincludes operator means for effecting operation of said second and thirdactuator means, said second actuator means includes a first linkoperatively connected to said one of said hydrostatic transmissions andfirst coupling means operatively interconnecting said operator means andsaid first link for transmitting forces from said drive means to saidfirst link only in response to movement of said control member in one ofsaid two directions, said third actuator means including a second linkoperatively connected to said other of said hydrostatic transmissionsand second coupling means operatively interconnecting said operatormeans and said second link for transmitting force from said drive meansto said second link only in response to movement of said control memberin the other of said two directions.

13. Apparatus as set forth in claim 10 further including selectivelyactuatable retaining means for retaining said first actuating means inan operating position corresponding to selected operating speeds foreach of said hydrostatic transmissions while allowing said second andthird actuator means to be operated to vary the speeds of operation ofsaid hydrostatic transmissions relative to each other and the selectedoperating speeds.

M. Apparatus for controlling the operation of a plurality of hydrostatictransmissions, said apparatus comprising a single control memberoperable-in a plurality of directions relative to an initial positionfor controlling the speed and direction of operation of said hydrostatictransmissions, and mechanical linkage means comprising a plurality ofmechanically interconnected links for operatively interconnecting saidcontrol member and said hydrostatic transmissions, said mechanicallinkage means being responsive to operation of said control member in afirst direction from said initial position to effect operation of saidhydrostatic transmissions in a forward direction at substantially thesame speed which is variable by varying the extent of operation of saidcontrol member in the first direction, said mechanical linkage meansbeing responsive to operation of said control member in a seconddirection from said initial position to effect operation of saidhydrostatic transmissions in a reverse direction at substantially thesame speed which is variable by varying the extent of operation of saidcontrol member in the second direction, said mechanical linkage meansbeing responsive to operation of said control member in a thirddirection after operation of said control member in said first directionfrom said initial position to effect a decrease in the speed ofoperation of one of said hydrostatic transmissions relative to anotherof said hydrostatic transmissions, said mechanical linkage means beingresponsive to operation of said control member in said third directionafter operation of said control member in said second direction fromsaid initial position to effect a decrease in the speed of operation ofsaid one of said hydrostatic transmissions relative to said other ofsaid hydrostatic transmissions,

said linkage means comprising first and second actuator links mountedfor pivotal movement about a common axis,

first and second connector rods pivotally connected to said first andsecond actuator links respectively for actuation thereby upon movementthereof,

the pivotal connection between said first actuator link and said firstconnector rod and said second actuator link and said second connectorrod lying on said common axis when said control member is disposed insaid third direction from said initial position.

15. Apparatus as set forth in claim 14 wherein said control member isoperated in said first and second directions by rotating said controlmember about a first axis and said control member is operated in saidthird direction by rotating said control member about a second axisextending transversely to said first axis.

16. Apparatus as set forth in claim 14 wherein said mechanical linkagemeans is responsive to operation of said control member in a fourthdirection opposite to said third direction after operation of saidcontrol member in said first direction from said initial position toeffect a decrease in the speed of operation of said other hydrostatictransmission relative to said one hydrostatic transmission, saidmechanical linkage means being responsive to operation of said controlmember in said fourth direction after operation of said control memberin said second direction from said initial position to efiect a decreasein the speed of operation of said other hydrostatic transmissionrelative to said one hydrostatic transmission.

17. Apparatus as set forth in claim 16 wherein said hydrostatictransmissions are ineffective for transmitting power when said controlmember is in said initial position, said mechanical linkage means beingineffective to change the speed of operation of said hydrostatictransmissions relative to each other in response to operation of saidcontrol member in either said third or said fourth direction when saidcontrol member is in said initial position.

18. Apparatus as set forth in claim 16 further including a plurality ofgears operatively connecting said control member with said mechanicallinkage means, said gears being retained against rotation relative toeach other while being rotated about a the same axis upon operation ofsaid control member in said first or said second direction, said gearsbeing rotated relative to each other upon operation of said controlmember in either said third or said fourth direction to effect a changein speed of one of said hydrostatic transmissions relative to the other.

19. Apparatus for controlling the operation of a plurality ofhydrostatic transmissions, said apparatus comprising a singlecontrolmember operable in a plurality of directions relative to an initialposition for controlling the speed and direction of operation of saidhydrostatic transmissions, and mechanical linkage means comprising aplurality of mechanically interconnected links for operativelyinterconnecting said control member and said hydrostatic transmissions,said mechanically interconnected links including a first actuator linkwhich is operated in response to operation of said control member in afirst direction from said initial position to effect operation of saidhydrostatic transmissions in the forward direction at the same speed andwhich is operated in response to operation of said control member in asecond direction from said initial position to effect operation of saidhydrostatic transmissions in the reverse direction at the same speed, asecond actuator link which is operated in response to operation of saidcontrol member in a third direction to effect a change in the speed ofsaid one hydrostatic transmission relative to said other hydrostatictransmission only when said control member is dis placed in either saidfirst or second direction from said initial position and a thirdactuator link which is operated in response to operation of said controlmember in a fourth direction to effect a change in the speed of saidother hydrostatic transmission relative to said one hydrostatictransmission only when said control member is displaced in either saidfirst or second direction from said initial position.

20. Apparatus as set forth in claim 19 wherein said mechanical linkagemeans further comprises first linkage means for operatively connectingsaid mechanically interconnected links with said one hydrostatictransmission and second linkage means for operatively connecting saidmechanically interconnected links with said other hydrostatictransmission, and said mechanically interconnected links of saidmechanical linkage means further comprises a first connector linkinterconnecting said second actuator link and said first linkage meansand a second connector link interconnecting said third actuator link andsaid second linkage means, said second actuator link and said firstconnector link being pivotal about a first axis in response to movementof said control member in said third direction when said control memberis in said initial position in such a manner that said second actuatorlink is ineffective to operate said first linkage means to change thespeed of said one hydrostatic transmission relative to said otherhydrostatic transmission, said third actuator link and said secondconnector link being pivotal about a second axis in response to movementof said control member in said fourth direction when said control memberis in said initial position in such a manner that said third actuatorlink is ineffective to operate said second linkage means to change thespeed of operation of said other hydrostatic transmission relative tosaid one hydrostatic transmission.

21. Apparatus as set forth in claim 20 wherein said second and thirdactuator links are pivotally mounted on said first actuator link andoperation of said first actuator link in response to movement of saidcontrol member in either said first or second directions pivots saidsecond and third actuator links about a third axis to actuate said firstand second linkage means through said first and second connector linksto effect a change in the speed of operation of said hydrostatictransmissions.

22. Apparatus as set forth in claim 19 wherein said linkage meansfurther comprises first connection means operatively interconnectingsaid second actuator link and said control member for enabling saidcontrol member to effect actuation of said second actuator link uponoperation of said control member in said third direction after operationof said control member in either said first or said second directionfrom said initial position and for rendering said control memberineffective to actuate said second actuator link upon operation of lidsaid control member in said fourth direction after operation of saidcontrol member in either said first or said second direction from saidinitial position, and second connection means operativelyinterconnecting said third actuator link and said control member forenabling said control member to effect actuation of said third actuatorlink upon operation of said control member in said fourth directionafter operation of said control member in either said first or seconddirection from said initial position and for rendering said controlmember ineffective to actuate said third actuator link upon operation ofsaid control member in said third direction after operation of saidcontrol member in either said first or said second direction from saidinitial position.

23. Apparatus as set forth in claim 19 further including means forretaining said first actuator link in an operated conditioncorresponding to a selected speed of operation of said hydrostatictransmissions in either the forward or reverse directions and enablingsaid second and third actuator links to be operated upon operation ofsaid control member in either said third or fourth direction to vary thespeed of said hydrostatic transmissions relative to each other.

24. In an apparatus for controlling the operation of a plurality ofhydrostatic transmissions, said apparatus including a first actuatorlink having an initial position, a second actuator link operativelyconnected to said first actuator link and one of said hydrostatictransmissions, a third actuator link operatively connected to said firstactuator link and to another of said hydrostatic transmissions, firstactuator means for operating said first actuator link in a firstdirection from the initial position to operate said second and thirdactuator links and thereby effect operation of said hydrostatictransmissions in a forward direction at substantially the same speedwhich is variable by varying the extent of operation of said first actuator link in said first direction and for operating said first actuatorlink in a second direction from the initial position to operate saidsecond and third actuator links and thereby effect operation of saidhydrostatic transmissions in a reverse direction at substantially thesame speed which is variable by varying the extent of operation of saidfirst actuator link in said second direction, and second actuator meansoperable in a first direction, and second actuator means operable in afirst direction from an initial condition for operating said secondactuator link to vary the speed of said one hydrostatic transmissionrelative to said other hydrostatic transmission and operable in a seconddirection from an initial condition for operating said third actuatorlink to vary the speed of said other hydrostatic transmission relativeto said one hydrostatic transmission, the improvement which comprisesconnector means operatively interconnecting said second actuator meansand said second and third actuator links for enabling said secondactuator means to operate said second actuator means to operate saidsecond actuator link upon operation of said second actuator means in thefirst direction from its initial condition to vary the speed of said onehydrostatic transmission while maintaining substantially constant thespeed of said other hydrostatic transmission and for enabling saidsecond actuator means to operate said third actuator link upon operationof said second actuator means from in the second direction from itsinitial condition to vary the speed of said other hydrostatictransmission while maintaining substantially constant the speed of saidone hydrostatic transmission.

25. Apparatus as set forth in claim 24 further comprising asingle-control member movable in a plurality of directions for effectingoperation of said first and second actuator means.

26. Apparatus for controlling the operation of a plurality ofhydrostatic transmissions for driving a vehicle to thereby control thespeed and direction of movement of the vehicle, said apparatuscomprising a single-control member operable in a plurality of directionsrelative to an initial position to vary the speed and direction ofoperation of said hydrostatic transmissions to thereby vary thedirection and speed of forward, forward-taming, reverse andreverse-turning movement of the vehicle, and mechanical linkage meanscomprising a plurality of mechanically interconnected links foreffecting operation of said hydrostatic transmissions to vary the speedand direction of forward, forward-turning, reverse and reversetumingmovement of the vehicle in a manner which corresponds directly to thedirection of operation of said control member,

said mechanical linkage means comprising,

first and second actuator links mounted for pivotal movement about acommon axis,

first and second connector rods pivotally connected to said first andsecond actuator links respectively for actuation thereby upon movementthereof,

the pivotal connection between said first actuator link and said firstconnector rod and said second actuator link and said second connectorrod lying on said common axis when said control member is disposed insaid third direction from said initial position,

said pivotal connection moving off of said common axis when said controlmember is disposed forwardly or rever sely from said initial position.

27. Apparatus as set forth in claim 26 wherein said control member is ajoystick.

28. Apparatus as set forth in claim 26 wherein said control member is aT-handle.

29. Apparatus as set forth in claim 26 wherein said control member hasan initial position said mechanical linkage effects the operation ofsaid hydrostatic transmissions to interrupt the vehicle drive, saidcontrol member being operable in a plurality of directions from saidinitial position while maintaining the vehicle drive in an interruptedcondition.

30. in an apparatus for controlling the operation of a plurality ofhydrostatic transmissions, said apparatus comprising a first actuatorlink having an initial position, a second actuator link operativelyconnected to said first actuator link and one of said hydrostatictransmissions, a third actuator link operatively connected to said firstactuator link and to another of said hydrostatic transmissions, firstactuator means for operating said first actuator link in a firstdirection from the initial position to operate said second and thirdactuator links and thereby effect operation of said hydrostatictransmissions in a forward direction at substantially the same speedwhich is variable by varying the extent of operation of said firstactuator link in said first direction and for operating said firstactuator link in a second direction from the initial position to operatesaid second and third actuator links and thereby effect operation ofsaid hydrostatic transmissions in a reverse direction at substantiallythe same speed which is variable by varying the extent of operation ofsaid first actuator link in said second direction, and second actuatormeans operable in a first direction from an initial condition foroperating said second actuator link to vary the speed of said onehydrostatic transmission relative to said other hydrostatic transmissionand operable in a second direction from an initial condition foroperating said third actuator link to vary the speed of said otherhydrostatic transmission relative to said one hydrostatic transmission,the improvement which comprises:

said second and third actuator links being pivotally connected with saidfirst actuator link and being rotatable about a first axis under theinfluence of said first actuator link upon operation of said firstactuator means,

said second actuator link being pivotable about a second axis uponoperation of said second actuator means in the first direction from itsinitial position, and said third actuator link being pivotable about thesecond axis upon operation of said second actuator means in the seconddirection from its initial position.

31. in an apparatus for controlling the operation of a plurality ofhydrostatic transmissions, said apparatus comprising a first actuatorlink having an initial position, a second actuator link operativelyconnected to said first actuator link and one of said hydrostatictransmissions, a third actuator link operatively connected to said firstactuator link and to another of said hydrostatic transmissions, firstactuator means for operating said first actuator link in a firstdirection from the initial position to operate said second and thirdactuator links and thereby effect operation of said hydrostatictransmissions in a forward direction at substantially the same speedwhich is variable by varying the extent of operation of said firstactuator link in said first direction and for operating said firstactuator link in a second direction from the initial position to operatesaid second and third actuator links and thereby effect operation ofsaid hydrostatic transmissions in a reverse direction at substantiallythe same speed which is variable by varying the extent of operation ofsaid first actuator link in said second direction, and second actuatormeans operable in a first direction from an initial condition foroperating said second actuator link to vary the speed of said onehydrostatic transmission relative to said other hydrostatic transmissionand operable in a second direction from an initial condition foroperating said third actuator link to vary the speed of said otherhydrostatic transmission relative to said one hydrostatic transmission,the improvement which comprises:

a first connector link operatively connected with said second actuatorlink, first linkage means pivotally connected to said first connectorlink for operatively connecting said first connector link and saidsecond actuator link with said one hydrostatic transmission, a secondconnector link operatively connected with said third actuator link, andsecond linkage means pivotally connected to said second connector linkfor operatively connecting said second connector link and said secondactuator link with said other hydrostatic transmission, said pivotconnection between said first connector link and said first linkagemeans being coaxial with a pivot connection between said second actuatorlink and said first actuator link when said first actuator link is inits initial position so that pivotal movement of said second actuatorlink under the influence of said second actuator means is ineffective toeffect operation of said one hydrostatic transmission through said firstconnector link and said first linkage means, said pivot connectionbetween said second connector link and said second linkage means beingcoaxial with a pivot connection between said third actuator link andsaid first actuator link when said first actuator link is in its initialposition so that pivotal movement of said third actuator link under theinfluence of said second actuator means is ineffective to effectoperation of said other hydrostatic transmission through said secondconnector link and said second linkage means.

1. Apparatus for controlling the operation of a plurality of hydrostatictransmissions, said apparatus comprising a singlecontrol member movablein a plurality of directions from an initial position for controllingthe speed and direction of operation of said hydrostatic transmissionsand for varying the speed of operation of said hydrostatic transmissionsrelative to each other, and linkage means for connecting said controlmember to said hydrostatic transmissions in such a manner that movementof said control member in either one of two lateral directions relativeto said initial position is ineffective to vary the operation of saidhydrostatic transmissions, said linkage means comprising, first andsecond actuator links mounted for pivotal movement about a common axis,first and second connector rods pivotally connected to said first andsecond actuator links respectively for actuation thereby upon movementthereof, the pivotal connection between said first actuator link andsaid first connector rod and said second actuator link and said secondconnector rod lying on said common axis when said control member isdisposed in either lateral direction from said initial position. 2.Apparatus as set forth in claim 1 wherein at least one of said actuatorlinks is movable about a first axis in response to movement of saidcontrol member in any one of said plurality of directions to therebyeffect a variation in the operation of one of said hydrostatictransmissions, said actuator link being movable about said common axisin response to movement of said control member in either one of said twolateral directions from said initial position without varying theoperation of said one hydrostatic transmission.
 3. Apparatus as setforth in claim 2 wherein the other actuator link is movable about afirst axis in response to movement of said control member in any one ofsaid plurality of directions to thereby effect a variation in theoperation of another of said hydrostatic transmissions, said otheractuator link being movable about said common axis in response tomovement of said control member in either one of said two directionsfrom said initial position without varying the operation of said otherhydrostatic transmission.
 4. Apparatus as set forth in claim 3 whereinsaid first axis about which said actuator links rotate are coaxial. 5.Apparatus as set forth in claim 1 wherein movement of said controlmember in a first one of said plurality of directions effects operationof said hydrostatic transmissions at substantially the same speed in onedirection, said control member being movable in a second one of saidplurality of directions to effect operation of said hydrostatictransmissions at substantially the same speed in another directionopposite from said one direction, said control member being movable in athird one of said plurality of directions which is lateral to a path ofmovement of said control member in said first and second directions toeffect operation of one of said hydrostatic transmissions at a greaterspeed in said one direction than the speed at which another of saidhydrostatic transmissions is operated in said one direction, and saidcontrol member being movable in a fourth one of said plurality ofdirections which is lateral of said path of movement of said controlmember to effect operation of said one hydrostatic transmission at agreater speed in said other direction than the speed at which another ofsaid hydrostatic transmissions is operated in said one direction. 6.Apparatus as set forth in claim 1 further including drive means foractuating said linkage means in response to movement of said controlmember in any one of said plurality of directions and in either of saidtwo lateral directions.
 7. Apparatus as set forth in claim 1 furtherincluding gear means operatively interconnecting said control member andsaid linkage means for actuating said linkage means in response tomovement of said control member in any one of said plurality ofdirections and in either of said two lateral directions.
 8. Apparatus asset forth in claim 1 wherein said control member is movable in saidplurality of directions from said initial position to a plurality ofoperating positions corresponding to various speeds and directions ofoperation of said hydrostatic transmissions, said control member beingmovable in at least one of said two lateral directions from any one ofsaid operating positions to vary the speed of at least one of saidhydrostatic transmissions relative to another of said hydrostatictransmissions.
 9. Apparatus as set forth in claim 8 further includingselectively actuatable retaining means for retaining said control memberagainst movement in any one of a plurality of directions from a selectedone of said operating positions while allowing said control member tomove in at least one of said two lateral directions from said selectedone of said operating positions.
 10. Apparatus for controlling theoperation of a plurality of hydrostatic transmissions, said apparatuscomprising a single-control member movable in a plurality of directionsfrom an initial position for controlling the speed and direction ofoperation of said hydrostatic transmissions and for varying the speed ofoperation of said hydrostatic transmissions relative to each other, andlinkage means for connecting said control member to said hydrostatictransmissions in such a manner that movement of said control member ineither one of two directions relative to said initial position isineffective to vary the operation of said hydrostatic transmissions,said linkage means including first actuator means for contemporaneouslyeffecting substantially equal variations in the operating speed of eachof said hydrostatic transmissions in response to movement of saidcontrol member, second actuator means for effecting variations in theoperating speed of one of said hydrostatic transmissions withouteffecting corresponding variations in the speed of another of saidplurality of hydrostatic transmissions, and third actuator means foreffecting variations in the operating speed of said other hydrostatictransmission without effecting corresponding variations in the speed ofsaid one hydrostatic transmission.
 11. Apparatus as set forth in claim10 wherein said second actuator means is actuated in response tomovement of said control member in one of said two directions and saidthird actuator means is actuated in response to movement of said controlmember in the other of said two directions.
 12. Apparatus as set forthin claim 10 wherein said linkage means includes operator means foreffecting operation of said second and third actuator means, said secondactuator means includes a first link operatively connected to said oneof said hydrostatic transmissions and first coupling means operativelyinterconnecting said operator means and said first link for transmittingforces from said drive means to said first link only in response tomovement of said control member in one of said two directions, saidthird actuator means including a second link operatively connected tosaid other of said hydrostatic transmissions and second coupling meansoperatively interconnecting said operator means and said second link fortransmitting force from said drive means to said second link only inresponse to movement of said control member in the other of said twodirections.
 13. Apparatus as set forth in claim 10 further includingselectively actuatable retaining means for retaining said firstactuating means in an operating position corresponding to selectedoperating speeds for each of said hydrostatic transmissions whileallowing said second and third actuator means to be operated to vary thespeeds of operation of said hydrostatic transmissions relative to eachother and the selected operating speeds.
 14. Apparatus for controllingthe operation of a plurality of hydrostatic transmissions, saidapparatus comprising a single control member operable in a plurality ofdirections relative to an initial position for controlling the speed anddirection of operation of said hydrostatic transmissions, and mechanicallinkage means comprising a plurality of mechanically interconnectedlinks for operatively interconnecting said control member and saidhydrostatic transmissions, said mechanical linkage means beingresponsive to operation of said control member in a first direction fromsaid initial position to effect operation of said hydrostatictransmissions in a forward direction at substantially the same speedwhich is variable by varying the extent of operation of said controlmember in the first direction, said mechanical linkage means beingresponsive to operation of said control member in a second directionfrom said initial position to effect operation of said hydrostatictransmissions in a reverse direction at substantially the same speedwhich is variable by varying the extent of operation of said controlmember in the second direction, said mechanical linkage means beingresponsive to operation of said control member in a third directionafter operation of said control member in said first direction from saidinitial position to effect a decrease in the speed of operation of oneof said hydrostatic transmissions relative to another of saidhydrostatic transmissions, said mechanical linkage means beingresponsive to operation of said control member in said third directionafter operation of said control member in said second direction fromsaid initial position to effect a decrease in the speed of operation ofsaid one of said hydrostatic transmissions relative to said other ofsaid hydrostatic transmissions, said linkage means comprising first andsecond actuator links mounted for pivotal movement about a common axis,first and second connector rods pivotally connected to said first andsecond actuator links respectively for actuation thereby upon movementthereof, the pivotal connection between said first actuator link andsaid first connector rod and said second actuator link and said secondconnector rod lying on said common axis when said control member isdisposed in said third direction from said initial position. 15.Apparatus as set forth in claim 14 wherein said control member isoperated in said first and second directions by rotating said controlmember about a first axis and said control member is operated in saidthird direction by rotating said control member about a second axisextending transversely to said first axis.
 16. Apparatus as set forth inclaim 14 wherein said mechanical linkage means is responsive tooperation of said control member in a fourth direction opposite to saidthird direction after operation of said control member in said firstdirection from said initial position to effect a decrease in the speedof operation of said other hydrostatic transmission relative to said onehydrostatic transmission, said mechanical linkage means being responsiveto operation of said control member in said fourth direction afteroperation of said control member in said second direction from saidinitial position to effect a decrease in the speed of operation of saidother hydrostatic transmission relative to said one hydrostatictransmission.
 17. Apparatus as set forth in claim 16 wherein saidhydrostatic transmissions are ineffective for transmitting power whensaid control member is in said initial position, said mechanical linkagemeans being ineffective to change the speed of operation of saidhydrostatic transmissions relative to each other in response tooperation of said control member in either said third or said fourthdirection when said control member is in said initial position. 18.Apparatus as set forth in claim 16 further including a plurality ofgears operatively connecting said control member with said mechanicAllinkage means, said gears being retained against rotation relative toeach other while being rotated about a the same axis upon operation ofsaid control member in said first or said second direction, said gearsbeing rotated relative to each other upon operation of said controlmember in either said third or said fourth direction to effect a changein speed of one of said hydrostatic transmissions relative to the other.19. Apparatus for controlling the operation of a plurality ofhydrostatic transmissions, said apparatus comprising a single-controlmember operable in a plurality of directions relative to an initialposition for controlling the speed and direction of operation of saidhydrostatic transmissions, and mechanical linkage means comprising aplurality of mechanically interconnected links for operativelyinterconnecting said control member and said hydrostatic transmissions,said mechanically interconnected links including a first actuator linkwhich is operated in response to operation of said control member in afirst direction from said initial position to effect operation of saidhydrostatic transmissions in the forward direction at the same speed andwhich is operated in response to operation of said control member in asecond direction from said initial position to effect operation of saidhydrostatic transmissions in the reverse direction at the same speed, asecond actuator link which is operated in response to operation of saidcontrol member in a third direction to effect a change in the speed ofsaid one hydrostatic transmission relative to said other hydrostatictransmission only when said control member is displaced in either saidfirst or second direction from said initial position and a thirdactuator link which is operated in response to operation of said controlmember in a fourth direction to effect a change in the speed of saidother hydrostatic transmission relative to said one hydrostatictransmission only when said control member is displaced in either saidfirst or second direction from said initial position.
 20. Apparatus asset forth in claim 19 wherein said mechanical linkage means furthercomprises first linkage means for operatively connecting saidmechanically interconnected links with said one hydrostatic transmissionand second linkage means for operatively connecting said mechanicallyinterconnected links with said other hydrostatic transmission, and saidmechanically interconnected links of said mechanical linkage meansfurther comprises a first connector link interconnecting said secondactuator link and said first linkage means and a second connector linkinterconnecting said third actuator link and said second linkage means,said second actuator link and said first connector link being pivotalabout a first axis in response to movement of said control member insaid third direction when said control member is in said initialposition in such a manner that said second actuator link is ineffectiveto operate said first linkage means to change the speed of said onehydrostatic transmission relative to said other hydrostatictransmission, said third actuator link and said second connector linkbeing pivotal about a second axis in response to movement of saidcontrol member in said fourth direction when said control member is insaid initial position in such a manner that said third actuator link isineffective to operate said second linkage means to change the speed ofoperation of said other hydrostatic transmission relative to said onehydrostatic transmission.
 21. Apparatus as set forth in claim 20 whereinsaid second and third actuator links are pivotally mounted on said firstactuator link and operation of said first actuator link in response tomovement of said control member in either said first or seconddirections pivots said second and third actuator links about a thirdaxis to actuate said first and second linkage means through said firstand second connector links to effect a change in the speed of operationOf said hydrostatic transmissions.
 22. Apparatus as set forth in claim19 wherein said linkage means further comprises first connection meansoperatively interconnecting said second actuator link and said controlmember for enabling said control member to effect actuation of saidsecond actuator link upon operation of said control member in said thirddirection after operation of said control member in either said first orsaid second direction from said initial position and for rendering saidcontrol member ineffective to actuate said second actuator link uponoperation of said control member in said fourth direction afteroperation of said control member in either said first or said seconddirection from said initial position, and second connection meansoperatively interconnecting said third actuator link and said controlmember for enabling said control member to effect actuation of saidthird actuator link upon operation of said control member in said fourthdirection after operation of said control member in either said first orsecond direction from said initial position and for rendering saidcontrol member ineffective to actuate said third actuator link uponoperation of said control member in said third direction after operationof said control member in either said first or said second directionfrom said initial position.
 23. Apparatus as set forth in claim 19further including means for retaining said first actuator link in anoperated condition corresponding to a selected speed of operation ofsaid hydrostatic transmissions in either the forward or reversedirections and enabling said second and third actuator links to beoperated upon operation of said control member in either said third orfourth direction to vary the speed of said hydrostatic transmissionsrelative to each other.
 24. In an apparatus for controlling theoperation of a plurality of hydrostatic transmissions, said apparatusincluding a first actuator link having an initial position, a secondactuator link operatively connected to said first actuator link and oneof said hydrostatic transmissions, a third actuator link operativelyconnected to said first actuator link and to another of said hydrostatictransmissions, first actuator means for operating said first actuatorlink in a first direction from the initial position to operate saidsecond and third actuator links and thereby effect operation of saidhydrostatic transmissions in a forward direction at substantially thesame speed which is variable by varying the extent of operation of saidfirst actuator link in said first direction and for operating said firstactuator link in a second direction from the initial position to operatesaid second and third actuator links and thereby effect operation ofsaid hydrostatic transmissions in a reverse direction at substantiallythe same speed which is variable by varying the extent of operation ofsaid first actuator link in said second direction, and second actuatormeans operable in a first direction from an initial condition foroperating said second actuator link to vary the speed of said onehydrostatic transmission relative to said other hydrostatic transmissionand operable in a second direction from an initial condition foroperating said third actuator link to vary the speed of said otherhydrostatic transmission relative to said one hydrostatic transmission,the improvement which comprises connector means operativelyinterconnecting said second actuator means and said second and thirdactuator links for enabling said second actuator means to operate saidsecond actuator means to operate said second actuator link uponoperation of said second actuator means in the first direction from itsinitial condition to vary the speed of said one hydrostatic transmissionwhile maintaining substantially constant the speed of said otherhydrostatic transmission and for enabling said second actuator means tooperate said third actuator link upon operation of said second actuatormeans fRom in the second direction from its initial condition to varythe speed of said other hydrostatic transmission while maintainingsubstantially constant the speed of said one hydrostatic transmission.25. Apparatus as set forth in claim 24 further comprising asingle-control member movable in a plurality of directions for effectingoperation of said first and second actuator means.
 26. Apparatus forcontrolling the operation of a plurality of hydrostatic transmissionsfor driving a vehicle to thereby control the speed and direction ofmovement of the vehicle, said apparatus comprising a single-controlmember operable in a plurality of directions relative to an initialposition to vary the speed and direction of operation of saidhydrostatic transmissions to thereby vary the direction and speed offorward, forward-turning, reverse and reverse-turning movement of thevehicle, and mechanical linkage means comprising a plurality ofmechanically interconnected links for effecting operation of saidhydrostatic transmissions to vary the speed and direction of forward,forward-turning, reverse and reverse-turning movement of the vehicle ina manner which corresponds directly to the direction of operation ofsaid control member, said mechanical linkage means comprising, first andsecond actuator links mounted for pivotal movement about a common axis,first and second connector rods pivotally connected to said first andsecond actuator links respectively for actuation thereby upon movementthereof, the pivotal connection between said first actuator link andsaid first connector rod and said second actuator link and said secondconnector rod lying on said common axis when said control member isdisposed in said third direction from said initial position, saidpivotal connection moving off of said common axis when said controlmember is disposed forwardly or reversely from said initial position.27. Apparatus as set forth in claim 26 wherein said control member is ajoystick.
 28. Apparatus as set forth in claim 26 wherein said controlmember is a T-handle.
 29. Apparatus as set forth in claim 26 whereinsaid control member has an initial position said mechanical linkageeffects the operation of said hydrostatic transmissions to interrupt thevehicle drive, said control member being operable in a plurality ofdirections from said initial position while maintaining the vehicledrive in an interrupted condition.
 30. In an apparatus for controllingthe operation of a plurality of hydrostatic transmissions, saidapparatus comprising a first actuator link having an initial position, asecond actuator link operatively connected to said first actuator linkand one of said hydrostatic transmissions, a third actuator linkoperatively connected to said first actuator link and to another of saidhydrostatic transmissions, first actuator means for operating said firstactuator link in a first direction from the initial position to operatesaid second and third actuator links and thereby effect operation ofsaid hydrostatic transmissions in a forward direction at substantiallythe same speed which is variable by varying the extent of operation ofsaid first actuator link in said first direction and for operating saidfirst actuator link in a second direction from the initial position tooperate said second and third actuator links and thereby effectoperation of said hydrostatic transmissions in a reverse direction atsubstantially the same speed which is variable by varying the extent ofoperation of said first actuator link in said second direction, andsecond actuator means operable in a first direction from an initialcondition for operating said second actuator link to vary the speed ofsaid one hydrostatic transmission relative to said other hydrostatictransmission and operable in a second direction from an initialcondition for operating said third actuator link to vary the speed ofsaid other hydrostatic transmission relative to said one hydRostatictransmission, the improvement which comprises: said second and thirdactuator links being pivotally connected with said first actuator linkand being rotatable about a first axis under the influence of said firstactuator link upon operation of said first actuator means, said secondactuator link being pivotable about a second axis upon operation of saidsecond actuator means in the first direction from its initial position,and said third actuator link being pivotable about the second axis uponoperation of said second actuator means in the second direction from itsinitial position.
 31. In an apparatus for controlling the operation of aplurality of hydrostatic transmissions, said apparatus comprising afirst actuator link having an initial position, a second actuator linkoperatively connected to said first actuator link and one of saidhydrostatic transmissions, a third actuator link operatively connectedto said first actuator link and to another of said hydrostatictransmissions, first actuator means for operating said first actuatorlink in a first direction from the initial position to operate saidsecond and third actuator links and thereby effect operation of saidhydrostatic transmissions in a forward direction at substantially thesame speed which is variable by varying the extent of operation of saidfirst actuator link in said first direction and for operating said firstactuator link in a second direction from the initial position to operatesaid second and third actuator links and thereby effect operation ofsaid hydrostatic transmissions in a reverse direction at substantiallythe same speed which is variable by varying the extent of operation ofsaid first actuator link in said second direction, and second actuatormeans operable in a first direction from an initial condition foroperating said second actuator link to vary the speed of said onehydrostatic transmission relative to said other hydrostatic transmissionand operable in a second direction from an initial condition foroperating said third actuator link to vary the speed of said otherhydrostatic transmission relative to said one hydrostatic transmission,the improvement which comprises: a first connector link operativelyconnected with said second actuator link, first linkage means pivotallyconnected to said first connector link for operatively connecting saidfirst connector link and said second actuator link with said onehydrostatic transmission, a second connector link operatively connectedwith said third actuator link, and second linkage means pivotallyconnected to said second connector link for operatively connecting saidsecond connector link and said second actuator link with said otherhydrostatic transmission, said pivot connection between said firstconnector link and said first linkage means being coaxial with a pivotconnection between said second actuator link and said first actuatorlink when said first actuator link is in its initial position so thatpivotal movement of said second actuator link under the influence ofsaid second actuator means is ineffective to effect operation of saidone hydrostatic transmission through said first connector link and saidfirst linkage means, said pivot connection between said second connectorlink and said second linkage means being coaxial with a pivot connectionbetween said third actuator link and said first actuator link when saidfirst actuator link is in its initial position so that pivotal movementof said third actuator link under the influence of said second actuatormeans is ineffective to effect operation of said other hydrostatictransmission through said second connector link and said second linkagemeans.